Electricity · Physics

Charge is conserved—and it explains what “charged” means.

Electricity begins with a simple accounting principle: charge does not appear or disappear in ordinary processes. This topic builds a clean conceptual model for how objects gain, lose, and rearrange charge.

This topic

Electric Charge

Define the properties of charge, distinguish conductors from insulators, and learn charging by contact and induction.

Properties

What charge is (and what it is not)

Electric charge is a property of matter that determines how it interacts electromagnetically. It comes in two signs, is quantized, and is measured in coulombs.

Two signs: positive and negative
Quantization: charge comes in discrete units
Units and scale: the coulomb is a large unit
Neutral means equal positive and negative total

Law

Conservation of charge

In ordinary physical processes, total charge in an isolated system is conserved. Charge can move and separate, but it does not vanish or appear from nothing.

What “isolated system” means in practice
Charge transfer vs charge creation
Conservation as a bookkeeping tool
Common examples: rubbing, contact, grounding

Materials

Conductors vs insulators

Whether charge moves freely depends on the material. Conductors allow charges to redistribute easily; insulators tend to “lock” charge in place.

Mobile charges in conductors (electrons in metals)
Insulators: charges are bound to atoms/molecules
Charging patterns on conductors (surface redistribution)
Role of grounding as a charge reservoir

Charging

Contact and induction

Objects become charged by transferring charge (contact) or by redistributing charge using a nearby charge (induction). Induction is often misunderstood; it is about separation first.

Charging by contact: direct transfer
Charging by induction: separation without touching
Grounding step and why it matters
Predicting final sign in common setups

Practice

Practice & Exercises

Practice predicting signs, tracking charge conservation, and reasoning about how conductors and insulators respond in charging scenarios.

Concept checks: sign, neutrality, quantization
Charge conservation bookkeeping problems
Conductor/insulator behavior predictions
Induction sequences: what changes at each step
Exam-style charging scenarios